1. Field of the Invention
The present invention relates to crash-survivable enclosures for data memory units used in aircraft and other vehicles operating over land and water. More particularly, the invention is directed to a retention device for use in a crash-survivable enclosure.
2. Description of the Prior Art
Solid state memory devices have been used in data recorders for recording essential data or information useful in determining causes of crashes or other mishaps in aircraft and other vehicles. When a crash occurs, it is essential that the recorded information on board survive the crash and subsequent events including heat, cold, flame, and fire that may afterwards ensue. In the event that the crash occurs over the ocean or other large body of water, the recorded information must be protected from the hydraulic pressure effects of deep water submersion.
Generally, it is desirable to protect voice and operational data supplied to the memory unit during a predetermined time interval immediately prior to a crash. In this regard, in order to preserve the data, the memory unit must be enclosed in a protective device configured and arranged to withstand temperatures in excess of 1,100.degree. C. (approximately 2,000.degree. F.) experienced during a fire and pressures up to 8,660 psi experienced at ocean depths of up to 20,000 feet. Simultaneously, the enclosure must be constructed to endure crushing and penetration forces experienced either on impact or during secondary impact with other portions or pieces of the vehicle.
Typical enclosures designed to meet these constraints are usually bulky, hemispherical enclosures, which have large space, weight, and power requirements. These requirements generally prohibit the use of most crash-survivable enclosures in small vehicles such as, general aviation aircraft, railroad passenger/cargo cars, buses, or cargo trucks.
Suitable access to the data memory unit is yet another design constraint that tends to drive size and shape requirements for typical enclosures. A removable door or panel, which provides access to the data memory unit, must be fastened to the enclosure without reducing the enclosure's ability to endure a crash. In ordinary crash-survivable enclosures, an access panel is typically bolted down into threads on the main body of the enclosure or onto a flange or similar mounting surface. The flange usually extends out beyond the circumferential surface of the enclosure and does not allow for venting. To maintain the structural integrity of the enclosure during a crash, the crash-survivable enclosures must be relatively large, with thick-walls to accommodate the threaded holes, fasteners and flanges.
In view of these limitations, a retention device is needed that can be used with a crash-survivable enclosure, which has a reduced size, a light weight, and a low power requirement. It would also be desirable to have a retention device that can secure an access panel to the enclosure without reducing the structural integrity of the enclosure and while removing the need for large, bulky flanges, thick-walled enclosure structures, and large numbers of fasteners.